Prosthetic heart valves with flexible leaflets, including those supported by a stent structure, are well known in the art. A variety of such prostheses are known for correcting problems associated with the cardiovascular system and in particular the heart. Therefore, the ability to replace or repair diseased heart valves with prosthetic devices has become a well-used method for treating heart valve deficiencies due to disease and congenital defects.
Prosthetic heart valve leaflets thus perform the function of opening and closing to regulate blood flow through the valve. These heart valve leaflets must therefore typically either pivot or flex with each cycle of the heart to open and close. The prostheses themselves have been constructed from natural materials such as tissues, synthetic materials, or combinations thereof. Prostheses formed from purely synthetic materials can, for example, be manufactured from biocompatible metals, ceramics, carbon materials, and polymers. In these cases, the leaflets can be either rigid or flexible in various embodiments.
Those heart valve prostheses which include flexible leaflets can be made from tissue leaflets or polymer leaflets. The use of polymer leaflets has become more desirable, particularly in accordance with the search for durable and stable leaflet performance over a number of years of use.
According to U.S. Pat. No. 6,953,332 (“the '332 Patent”) and U.S. Pat. No. 7,682,389 (“the '389 Patent”), dip coating methods and mandrels are used to form these polymer leaflets and valve prostheses. Such a mandrel is shown, for example FIG. 1 hereof, which corresponds to FIG. 8 of the '332 Patent, including an upper surface 314 and a number of contours 310 which correspond to the number of valve leaflets desired. The dip coating process disclosed in the '332 and '389 Patents is one in which the mandrel itself defines the leaflet profile or shape, and after the dipping process takes place, it is generally necessary to then conduct a trimming step in order to cut the extra polymer off along the free edge of the leaflet on the mandrel (see FIG. 7). This step, in turn, requires a precisely controlled apparatus with a cutting instrument applied to the leaflet and the mandrel. This, in turn, can cause defects on the leaflet at that cutting edge and on the mandrel as well, requiring precisely machined and polished mandrel surfaces which therefore must be abandoned after the trimming step. Indeed, this also restricts the type of materials which can be used for the mandrel itself, since mandrels made of certain materials such as stainless steel would not be suitable to be applied to particular cutting instruments used thereon.
These leaflets can also be dip-coated inside an associated collapsible stent, such as those in use in connection with trans-catheter aortic valve implantation (see FIG. 6). In this case, the trimming process becomes even more difficult, particularly where the leaflet is inside the cage-like stent, as shown in FIG. 6. Since in the currently used process the leaflet cannot be trimmed inside the strut-surrounded stent, the leaflet must be preformed, trimmed, and then removed from the mandrel, and then bonded to the stent with an additional step before both the polymer of the leaflet and the polymer coated on the stent are fully cured. This therefore results in a weaker bonding force between the leaflet and the stent which cannot satisfy the functional requirements of the valve and which provide for a much more complicated manufacturing process.
The search has therefore continued for a better manufacturing process for polymer stents, particularly in connection with the mandrel dipping process, and for potential trimming processes within the stent.